CAA NZ Basic Turbine Knowledge (Aeroplane) cheat sheet
CAA NZ Basic Turbine Knowledge (Aeroplane) · Keep the key ideas within reach.
Turbine engine fundamentals: Brayton cycle, thrust, efficiency, and engine station numbering
Brayton cycle: ideal thermal efficiency η = 1 − 1/(PR^((γ−1)/γ)), where PR = compressor pressure ratio and γ = specific heat ratio (≈1.4 for air).
Specific thrust = (F / ṁ) = (1 + f) V_e − V_0, where f = fuel-air ratio, V_e = exhaust velocity, V_0 = flight velocity.
Propulsive efficiency η_p = 2 V_0 / (V_e + V_0); thermal efficiency depends on overall pressure ratio and turbine entry temperature.
Station numbering (SAE ARP755): 0 = free stream, 1 = inlet entry, 2 = compressor inlet (LPC), 3 = compressor exit (HPC), 4 = combustor exit (turbine inlet), 5 = turbine exit, 7 = exhaust nozzle exit.
Thrust horsepower = F × V_0 / 550 (F in lbf, V_0 in ft/s); for turboprop, shaft horsepower plus jet thrust.
Overall pressure ratio (OPR) = P3 / P2; high OPR increases thermal efficiency but raises compressor exit temperature.
Turbine entry temperature (TET) limited by turbine blade material and cooling; typical modern TET 1500–1700 K.
Specific fuel consumption (SFC) = fuel flow / thrust; lower SFC indicates better efficiency.
Engine construction and major modules: compressor, combustor, turbine, shafts, bearings, and casings
Axial compressor stages consist of a rotor row followed by a stator row; each stage increases pressure and decreases axial velocity.
Centrifugal compressor: single-stage pressure ratio up to ~4:1; used in small engines or as high-pressure stage.
Combustor types: can, annular, and can-annular; annular most common in modern turbofans for compactness and uniform exit temperature.
Turbine blades: high-pressure turbine (HPT) often cooled; low-pressure turbine (LPT) drives fan or propeller via concentric shafts.
Shaft arrangements: single-spool (compressor and turbine on one shaft), twin-spool (LP and HP separate), triple-spool (e.g., RB211).
Bearings: ball bearings take radial and some axial loads; roller bearings take radial loads; thrust bearings absorb axial loads.
Casings: inlet casing, compressor casing, combustor casing, turbine casing, exhaust casing; provide structural support and airflow containment.
Accessory gearbox driven by HP spool via bevel gear; drives fuel pump, oil pump, hydraulic pump, generator, starter.
Lubrication and sealing systems: oil types, tanks, pumps, filters, coolers, and seals
Turbine oils: synthetic ester-based (MIL-PRF-23699) for high temperature stability; mineral oils used in older engines.
Oil tank: often pressurised by bleed air to prevent foaming at altitude; includes deaerator and expansion space.
Oil pumps: pressure pump (gear or vane) supplies oil to bearings; scavenge pumps return oil to tank; often multiple scavenge stages.
Oil filters: main filter with bypass valve; chip detectors (magnetic) in scavenge lines to detect metallic debris.
Oil coolers: air-cooled or fuel-cooled (fuel/oil heat exchanger); fuel-cooled reduces fuel icing and cools oil.
Seals: labyrinth (non-contact) seals at bearing compartments; carbon face seals for high-speed shafts; pressurisation prevents oil leakage.
Oil pressure indication: low pressure warning triggers if pressure falls below safe limit; oil temperature monitored for overheating.
Oil consumption: normal if within limits; excessive consumption indicates seal or internal leakage.
Fuel systems and controls: fuel metering, fuel control units, hydromechanical and electronic engine control (FADEC/EEC)
Fuel metering: hydromechanical fuel control unit (FCU) schedules fuel flow based on throttle position, compressor speed, and altitude.
FADEC (Full Authority Digital Engine Control) or EEC (Electronic Engine Control): computes fuel flow and variable geometry positions; hydromechanical backup may exist.
Fuel control modes: acceleration, deceleration, steady-state; prevents overtemp and flameout.
Fuel system components: boost pumps, fuel/oil heat exchanger, fuel filter, high-pressure fuel pump, fuel metering unit, fuel nozzles.
Fuel nozzles: simplex, duplex, or airspray; duplex provides good atomisation at low and high flows.
Fuel types: Jet A, Jet A-1 (kerosene), JP-8 (military); avoid water contamination and microbial growth.
Fuel flow indication: measured by fuel flow transmitter; used for flight planning and engine trend monitoring.
Electronic engine control redundancy: dual-channel FADEC with automatic switchover; fault codes recorded for maintenance.
Ignition and starting systems: igniters, exciters, starter types, and starting malfunctions
Ignition systems: high-energy capacitor discharge exciter feeds igniter plugs (two per engine typically).
Igniter types: annular gap, constricted arc, or glow plug; high-energy for altitude relight.
Starter types: air turbine starter (bleed air from APU or ground cart), electric starter, or cartridge starter.
Starting sequence: motoring (dry crank) to purge fuel, then ignition on, fuel on, light-off, acceleration to idle.
Starting malfunctions: hot start (EGT exceeds limit), hung start (stagnant RPM), wet start (no light-off but fuel present).
Hot start causes: excessive fuel, low starter power, ignition delay; action: cut fuel, continue motoring to clear.
Hung start causes: insufficient starter power, fuel control fault, compressor stall; action: abort start.
Starter duty cycle: limits on consecutive start attempts to prevent overheating; typically 2–3 attempts with cooling periods.
Indication and monitoring: EGT, N1/N2, torque, fuel flow, vibration, and exceedance awareness
EGT (Exhaust Gas Temperature): indicates turbine temperature; highest during start and takeoff; exceedance can damage turbine.
N1: low-pressure spool speed (fan speed); primary thrust parameter for turbofan.
N2: high-pressure spool speed; indicates core speed; used for starting and monitoring.
Torque: for turboprop/turboshaft, measured by torque sensor; indicates power output.
Fuel flow: indicates fuel consumption; used for range and engine health monitoring.
Vibration: monitored by vibration sensors; high vibration indicates imbalance, bearing damage, or foreign object damage.
Exceedance awareness: record any exceedance (EGT, N1, N2, torque) in engine log; may require maintenance action.
Trend monitoring: compare parameters over time to detect deterioration.
Propulsion system operation: thrust management, reverse thrust, and engine handling limitations
Thrust management: use of autothrottle or manual throttle; takeoff thrust set by EPR or N1 target.
Reverse thrust: deflects fan or exhaust gases forward; used for deceleration on ground; not for in-flight use.
Thrust reverser types: cascade, bucket, and pivoting door; must be stowed and locked for flight.
Engine handling limitations: avoid rapid throttle movements to prevent compressor stall or flameout.
Takeoff thrust: time-limited (e.g., 5 minutes); use of reduced thrust (derate) extends engine life.
Engine anti-ice: uses bleed air to heat inlet; increases fuel consumption and reduces thrust.
Crosswind and tailwind limits: affect engine operation and reverse thrust effectiveness.
Thrust levers: control fuel flow; reverse thrust levers separate or integrated.
Engine performance and limitations: ratings, derates, altitude/temperature effects, and engine failure modes
Flat rating: engine maintains rated thrust up to a break temperature; above that thrust decreases with temperature.
Derate: reduced takeoff thrust to extend engine life; achieved by reducing EGT or N1 target.
Altitude effects: thrust decreases with altitude due to lower air density; compressor performance changes.
Engine failure modes: compressor stall/surge, flameout, foreign object damage (FOD), bearing failure, turbine blade failure.
Compressor stall: caused by airflow disruption; symptoms include bang, EGT rise, N1 fluctuation; action: reduce throttle, may require shutdown.
Flameout: loss of combustion; causes include fuel starvation, icing, or extreme altitude; action: attempt relight.
Turbine blade failure: can cause severe damage; monitored by vibration and EGT.
Engine ratings: takeoff, maximum continuous, cruise; limitations in flight manual.
Auxiliary and accessory systems: APU, bleed air, anti-ice, and accessory gearbox drives
APU (Auxiliary Power Unit): small gas turbine providing electrical power, bleed air for starting, and air conditioning on ground.
APU bleed air: used for main engine starting and pneumatic systems; limited altitude for operation.
Bleed air: extracted from compressor stages for anti-ice, pressurisation, and air conditioning; reduces engine thrust.
Anti-ice systems: thermal (bleed air) for engine inlet and airframe; electrical for some components.
Accessory gearbox: driven by engine HP spool; provides power to pumps, generators, and starter.
APU starting: battery or ground power; APU generator provides AC power.
Bleed air leaks: can cause loss of cabin pressure or engine damage; monitored by sensors.
APU limitations: EGT and load limits; automatic shutdown on fault.
Maintenance, airworthiness, and defect reporting for turbine aeroplanes
Maintenance schedule: based on flight hours or cycles; includes borescope inspections, oil analysis, and filter checks.
Airworthiness directives (ADs): mandatory compliance; must be recorded in maintenance records.
Defect reporting: any engine malfunction or exceedance must be reported to maintenance and recorded in logbook.
Oil analysis: detects wear metals; trend monitoring for early failure detection.
Borescope inspection: examines compressor and turbine blades for cracks, erosion, and FOD without disassembly.
Engine logbook: records all maintenance, inspections, and repairs; required for airworthiness.
Service bulletins: manufacturer recommendations; may be mandatory if referenced by AD.
Return to service: after maintenance, engine must be tested and signed off by licensed engineer.
Safety, human factors, and operational knowledge relevant to turbine engine handling
Human factors: fatigue, complacency, and pressure can lead to errors in engine handling; use checklists.
Situational awareness: monitor engine parameters and warnings; respond promptly to exceedances.
Crew resource management (CRM): effective communication between pilots and ground crew during engine start.
Safety around engines: avoid ingestion hazards; maintain clearance from intake and exhaust.
Fire safety: engine fire detection and extinguishing systems; know procedures.
Error management: cross-check engine instruments; verify thrust settings.
Operational knowledge: understand engine limitations and emergency procedures.
Reporting culture: report incidents and near-misses to improve safety.